The present invention relates to a rotary viscous damper, and in particular to a rotary viscous damper having a housing surrounding a disc which provides a variable output torque dependent on position of the disc with respect to the housing.
In a rotary viscous damper, a disc is located within a housing which provides a gap between side walls of the housing and opposite sides of the disc. The disc is typically connected to a shaft at its centerline, the shaft protruding outwardly of the housing. The housing is typically arranged to rotate, or is fixed, independently of the shaft. A viscous fluid is applied within the housing to fill the gaps on opposite sides of the disc. Thus, the disc is rotated by the shaft directly and the housing either is fixed, if used as a rotational drag or brake, or if used as a vibration damper, is rotated by a shearing force of the highly viscous fluid caused by rotation of the disc. When used as a drag or brake, the housing is fixed to be stationary and the viscous fluid can apply a resistive torque to the rotation of the disc by the shaft. When used as a damper, the housing is free to rotate with the disc and shaft, the rotary inertia of the housing and viscous fluid dampening out shaft vibrations.
Magnitude of the resistive torque is dependent upon several parameters, one of which is the shear gap dimension between the disc and the housing. It is known generally to vary the shear gap dimension to vary the resistive torque, such as disclosed in U.S. Pat. Nos. 5,165,506 and 4,938,322.